This invention relates to control of engine evaporative emissions of hydrocarbons and to a low emission integrated air fuel module capable of containing such emissions.
Automobile manufacturers have gone to great lengths to reduce emissions created by the vehicles they manufacture. Many sources of emissions have been pursued. The two major sources of emissions are the exhaust emissions (or xe2x80x98tail pipe emissionsxe2x80x99) and the hydrocarbon or unburned fuel that evaporate from other sites on the vehicle (or xe2x80x98evaporative emissionsxe2x80x99). In today""s vehicles, fuel tanks are vented through carbon canisters so that hydrocarbons are removed from the air escaping from the tank due to pressure differentials. These evaporative emissions are stored until they can be pulled into the engine and consumed. This type of system is very effective at stopping hydrocarbon emissions from escaping from the fuel tank system.
There are sources other than the fuel tank that can contribute to the hydrocarbon evaporative emissions of a vehicle. One such source is the xe2x80x98breathingxe2x80x99 of the air induction system during hot soak and diurnal temperature cycling. Unburned fuel resident in the intake system after engine shutdown evaporates into the air in the system. Air exchanges, between the air induction system and the atmosphere, carry these evaporated hydrocarbon emissions into the atmosphere. Activated charcoal or xe2x80x98carbon adsorbersxe2x80x99 have previously been installed in air cleaner housings to reduce these hydrocarbon emissions. The carbon adsorber draws in and holds the hydrocarbons until the engine is started and the air flow past the adsorber pulls the hydrocarbons back into the engine and purges the adsorber.
Another common source of hydrocarbon emmissions is seal leakage of both high pressure and low pressure fuel components and systems. Current fuel delivery systems contain many such potential leak paths. These include O-rings, injector and fuel rail interfaces, fuel regulator diaphragm, end plugs, fuel rail inlet and outlet, service valve, and crankcase ventilation system interfaces and joints. Each of these locations has the potential of leaking emissions to the surrounding environment.
A third common source of hydrocarbon emissions to the atmosphere is permeation of the fuel through the materials of the system. Hydrocarbons can permeate most composite and elastomer materials commonly used in the automotive engine environment. Small amounts of hydrocarbons therefore leak through the walls of composite components in the system and through the elastomer O-rings and seals at the interfaces in the system. This leakage is increased with higher fuel pressures driving the hydrocarbons out through the walls.
The above contributors are generally small in relation to the total evaporative emissions of the vehicle and automobile manufacturers can meet the current standards without further development or control. However, in order to meet zero or near zero evaporative emissions requirements, engine suppliers and vehicle manufactures will have to reduce the number of leak and permeation sites that can emit hydrocarbons.
The present invention provides an integrated air fuel module for an internal combustion engine that reduces or eliminates the escape of hydrocarbon evaporative emissions from the integrated air fuel module system, sub systems and components. The integrated air fuel module of the present invention includes containment means, such as a valve or carbon adsorber, that blocks the escape of evaporated hydrocarbon emissions from the air inlet of an internal combustion engine during engine off conditions. The module provides a reduced number of potential external hydrocarbon leak and permeation paths to the surrounding atmosphere. Preferred geometries of the intake manifold in the module with the internal integration of other normally external systems, such as fuel injection and positive crankcase ventilation systems, accomplish the containment of evaporative emissions within or entering the air fuel module between engine operating periods when the engine is shut down.